Method of discharging carbon dioxide to inhibit the generation of electrostatic charges



METHOD OF 7 DISCHARGING- QARBON. DIOXIDE T .INHIBIT THE t GENERATION 0F ELECTRD- STATIC CHARGES (i. Gi'ziiit, Jifl, iiidgewood assignor to' Special es Development Corporat1oii; Belleviile; N. J., a cameras-6n immerse 7 No mwiid- Anih Edi. in d 3; 1 1; Serial No. 267,93 :3 v 2 claims; (cltz'sz' -s This invention relates it method of discharging carbon dioxide stored under 5 i e, an more particularly, to minimizing or elimiiia g be generation of static'electri city upon the discharge offthe cdrbon dioxide.

Carbon dioxide stored-tinder pressurein liquid and/or gaseous state is widelyiised asafire' guishing medium by discharging the same throiig'h a-sno forming shield or horn for d re'ctifig" an "n dioxide as the die. one of: such uses is' inconhection with portable fire extingui'shers adapted to be earned by the operator to the location of the fire. Such extinguishers generally corn-prise a coiitaiiier rating a 'diseha'rg'ectjritifol'yalve and a snow forming horn d to the outlet of'they'alve. The fluid banana (1 elente'rs the horn through a'no'zzle or orifice at a high yeloeit'y andis'expanded to produce a s'treai'n of earbon dioxide g'as 'a'nd snow in admixture, the horn serving to re'du e the 'yelecit y' of the carbon dioxide stream discharged 7 from the mouth Thereof whereby substantial entrainmentof 'air is prevented. Ane'xample of such an extinguisher is illustrated in United States Patent No. 1,760,274, issued-May 27, 1 930. n

In many instances upoiidischarging the carbon dioxide stored ina portable extinguisher, the operator-receives an electric shock due to the generationof static electricity believed to "be caused primarily by the violent collision of carbon dioxide snow' -particles against each "other and the inner walls of the horn.

Accordingly, an object-:of the presentf'invention is to overcome theforegoiiigidifiiculties' and objectionsby providing a methodof expanding and dischargihgjfluid'car bon dioxide'through a born or' shield which will prevent the generation for substantial" electrostatic charges.

Another object is'todischarg'ei an expanding stream of carbon dioxide-gas and snow Particlestogether withan electrostatic charge g enerating inhibitor.

standing of the illustrative embodiment about to be de scribed, or will be in dicat ed in the appended claims, and

various adVantagesQndt referred to herein will occur to one skilled in the armada:eitipleyfiimertiieiavehtion in practice.

These objects generally are accomplished by dissolvfluid carbondioxide under lubricating snow lformed'in 2. Aviation .andlrefri gera tien: nitiatin oils, silieh Unite States Paten a Patented Mar. 12, 1957 ice DSGFSO, fGtilf Oil 501" and E580 Indiana #11699, which are highly refined lubricating oils derived from petroleum. V i

3. solvesso, a product prepared synthetically from e roleum; containing chiefly aromatic hydrocarbons, for example, the" several types disclosed in Lubetext, published by Ihc., 1940. H

These materials are fluids having a low surface tension and the tendency to spread over the horn or shield surface to form a persistent frictionless film even at extremely low temperatures, for example at -135 F, which temperature is Within the usual temperature range of an expanding stream of carbon dioxide comprisinga mixture of snow particles; liquid and gas. Furthermore, the e materials are readily soluble or dispersible in liquid and/orgaseous carbon dioxide and are capable of existing in adily flowable state at temperatures of -5 F. and lbwei'; The approximate pour point temperatures of thes materials are; 7

Kerosene 40 to 50 F.

2. gayiatien and refrigeration type lubricating oils -5' to -20? F. p

nwin be understood that numerous other materials not set forth specifically herein but having the aforementioned physical properties couldlikewise be used to accomplish as oils sold inider'the tradehaime's tsreomerarneara the advantages of the present invention.

The caibon'dioxide used in providing the composition in accordance with the invention may be or" the commercial grade available in liquid state or in solid blocks of so called Dry Ice adapted to be converted into'liquid state. It is possible that commercial grades of carbon dioxide may' contain-slight traces of impurities which are introduced in conducting fluid carbon dioxide through lubricated "pipe joints or machineryparts and/ or by storingthe carbon dioxide in metallic containers treated with corrosion inhibiting compounds. Blocks of Dry Ice further may contain minute quantities of materials intended to promote or improve crystal growth or to serve as a plasticizer in forming the blocks. In so far as could'be determined, the amount of such impurities and/or additivesnever exceeds .-15% by'weight and usuallyison the orderof approximately .05 by weight.

it has been found that a minium of about .l% to by weight "of the additive materials'in accordance 'with the present invention,"singly or in admixture, is required to be addedto such carbon-dioxide to provide the-desired lubricating effecton the particles of carbon dioxide snow and the horn or shield-to-reduce friction and substantially eliminate or greatly minimize staticelectricity'so that it isnot perceptible to the operator upon discharging '-a fire extinguisher under conditions which'heretofore would have resulted ii -perceptible and objectionable shocks.

The minimum amount of lubricating material selected usually depends upon the percentage of impurities or other additives already present in the carbon dioxide which is to be treated to inhibit the generation of static electricity. For example, untreated carbon dioxide which contains .1 5'% by weight of such materials'requires the addition of about .1% to 2% by weight of a material in accordance with "the'i-nyention. On the other handyuntreated carbon dioxide which does not contain'such materials requires the addition of at least about '.2% .of a material in accordance with the invention. In any case, to effectively inhibit the 'g'eneration o'f static electricity, the treated -"carbon dioxide composition should contain a'minimum'of between 2% to ,35%'byweight"of' the additive material.

By using such percentages of material or mixturesstandard of 99.5% specifiedfor-carb on dioxide by the- United States Army Air Corps and other branches of the armed services. Also, by using relatively small quantities of materials or mixtures thereof, inflammable materials may be employed without danger of explosion and with out adversely affecting the fire extinguishing efiiciency of the carbon dioxide.

For example, liquid carbon dioxide having a purity between about 99.8% and 99.9% is commercially available, thus permitting the materials to be added thereto in amounts of from .3% to .4% by weight and still maintaining the purity of the carbon dioxide at about 99.5%.

The maximum quantity of these additive materials which can be used to inhibit the generation of static electricity does not appear to be critical, it being conceivable that any composition containing a major amount by weight of carbon dioxide and a minor amount by weight of oily material of the character specified herein can be expanded in a manner to substantially eliminate or greatly minimize static electricity. However, from a practical consideration based on the fact that the composition in accordance with the invention is primarily intended for use as a fire extinguishing medium, it is desirable not to adulterate the carbon dioxide to a point where it loses its fire extinguishing efiiciency by maintaining the additive material content at a low value. In this respect, preliminary tests indicated that by weight of these additive materials was permissible from a fire extinguishing viewpoint, but that preferably the quantity of such materials should not exceed about 1.6% by weight.

The present invention may thus be characterized in that the composition comprises a major quantity of carbon dioxide and a minor quantity of additive materialv present in an amount of at least .2% to 35% by weight of the composition and not exceeding 5% by weight but preferably not exceeding about 1.6% by weight.

In establishing the practical application of the present invention, the amounts of the materials set forth in the table were injected under pressure into about pounds of commercial grade liquid carbon dioxide stored at about 850 pounds per square inch in a container equipped with a discharge valve, a syphon tube, a snow forming horn and a hose connecting the valve and the horn to provide a portable carbon dioxide fire extinguisher of the usual type as referred to hereinbefore.

Table Additive Material Percent by Weight Kerosene (commercial grade) do {50% Kerosene (commercial grade).-

50% Esso Indiana 11699 85% Kerosene (Den-Base type) 15%dEsso Indiana 11699 The carbon dioxide compositions in accordance with Examples 1 to 38 were expanded from the nozzle and discharged through the horn by fully opening the valve, and such discharge required about 28 seconds, the discharge rate being about .5 pounds per second. The electrostatic charge and its potential were determined by the use of an electrostatic voltmeter and a microammeter, and it was found that in all cases the total electrostatic charge developed was not more than about 10 microcoulombs at a potential of between about 0 and 4.0 kilo-volts (kv.), the average potential being 1.3 kv.

Ten fire extinguishers of like construction and capacity containing 15 pounds of commercial grade liquid carbon dioxide, which was not treated in accordance with the that the untreated carbon dioxide contained slight traces of the usual impurities and/or materials to promote or. improve crystal growth or to act on a plasticizerin forming blocks of Dry Ice, these materials had no noticeable effect in inhibiting the generation of static electricity,

probably because they were present in insuflicient.

amounts.

While it is not intended to limit the invention to any particular theory, it is believed that the materials or mixtures used herein provide a lubricating film on the? surface of the snow particles formed and thereby greatly reduce friction upon collision of the particles against each other and the inner wall of the horn. 7

It is also contemplated that the materials may be added to the stream of carbon dioxide during its flow from the container to the discharge horn.

From the foregoing description, it will be seen that the present invention provides for substantially eliminating or greatly minimizing the generation of electrostatic; charges upon discharging carbon dioxide through a snowv forming horn in a novel manner. The inhibitors do not materially increase the cost of the carbon dioxide, dov not adversely affect the fire extinguishing properties of;

the carbon dioxide, can be injected into the carbon dioxide in a simple manner, and are effective upon discharging. the carbon dioxide at relatively high rates under conditions of low temperature and low relative humidity.

.As various changes may be made without departing from the scope and spirit of the invention, it will be understood that the details and examples hereinbeforc set forth are illustrative only and that the invention asbroadly described and claimed is in no way limited there- This application is a continuation-in-part of application for United States Letters Patent, Serial No. 677,511, filed June 18, 1946, now abandoned.

I claim:

1. The method of discharging a charge of fluid carbondioxide composition confined in a container under pressure from a nozzle through a shield to form carbon dioxide snow particles, which method comprises introducing into the carbon dioxide between at least about .2% but not exceeding 5% by weight of the composition of an oily hydrocarbon material having a low surface tension and being capable of existing in readily flowable state at a temperature of --5 F. and being capable of retaining its oily characteristics at a temperature of F.; and directing the carbon dioxide and the oily material in admixture therewith through the nozzle to form car'- bon dioxide snow particles in the shield whereby the snow particles and the interior of the shieldare coated with the oily material to form a persistent frictionless film on the interior of the shield adapted to inhibit the zeneration of electrostatic charges upon the flow of snow particles through the shield.

2. The method of discharging a charge of fluid carbon dioxide composition confined in a container under pressure from a nozzle through a shield to form carbon dioxide snow particles, the carbon dioxide having introduced therein between at least about .2% but not exceeding 5% by weight of the composition of an oily hydrocarbon material having a low surface tension and being capable of existing in readily flowable state at a temperature at 5 F. and being capable of retaining its oily characteristics at a temperature of -135 R, which method comprises directing the carbon dioxide and the oily material in admixture therewith through the orifice to form carbon dioxide snow particles in the shield whereby the snow particles and the interior of the shield are coated with References Cited in the file of this patent UNITED STATES PATENTS 2,020,189 Jones Nov. 5, 1935 FOREIGN PATENTS 453,084 Great Britain Sept. 4, 1936 OTHER 7 REFERENCES Carbon Dioxide, Quinn and Jones (1936), pub. by Reinhold Pub. Corp., New York, pp. 109-110. 

1. THE METHOD OF DISCHARGING A CHARGE OF FLUID CARBON DIOXIDE COMPOSITION CONFINED IN A CONTAINER UNDER PRESSURE FROM A NOZZLE THROUGH A SHIELD TO FORM CARBON DIOXIDE SNOW PARTICLES, WHICH METHOD COMPRISES INTRODUCING INTO THE CARBON DIOXIDE BETWEEN AT LEAST ABOUT 2% BUT NOT EXCEEDING 5% BY WEIGHT OF THE COMPOSITION OF AN OILY HYDROCARBON MATERIAL HAVING A LOW SURFACE TENSION AND BEING CAPABLE OF EXISTING IN READILY FLOWABLE STATE AT A TEMPERATURE OF -5*F. AND BEING CAPABLE OF RETAINING ITS OILY CHARACTERISTICS AT A TEMPERATURE OF -135*F., AND DIRECTING THE CARBON DIOXIDE AND THE OILY MATERIAL IN ADMIXTURE THEREWITH THROUGH THE NOZZLE TO FORM CARBON DIOXIDE SNOW PARTICLES IN THE SHIELD WHEREBY THE SNOW PARTICLES AND THE INTERIOR OF THE SHIELD ARE COATED WITH THE OILY MATERIAL TO FORM A PERSISTENT FRICTIONLESS FILM IN THE INTERIOR OF THE SHIELD ADAPTED TO INHIBIT THE GENERATION OF ELECTROSTATIC CHARGES UPON THE FLOW OF SNOW PARTICLES THROUGH THE SHIELD. 